That is not to suggest that Jose Mourinho's side are a one-man team – far from it – but Los Blancos boast a 76 per cent win rate in matches in which the Portuguese attacker has scored this season, while they have won just 28% of the games in which he has failed to find the back of the net.

Of the 14 matches in which Ronaldo has been neutralised, Madrid have won just four and those victories came against sides with an average La Liga position of 11.5. Stop Ronaldo, stop Real.

HOW THE TEAMS COULD LINE UP

Against both Bale and Fellaini, Sir Alex deployed Phil Jones in a holding role in front of the defence, tasked with tracking the players' runs

That is, of course, easier said than done. But there is a sense that Sir Alex Ferguson has been planning for the return of Old Trafford's prodigal son for some time and has used both Tottenham's Ronaldo prototype, Gareth Bale, and Everton's Marouane Fellaini as practice.

Against both players, Phil Jones was deployed in a holding role in front of the defence and was tasked with tracking the players' runs, double-teaming them and contesting aerial balls. Their influence waned as a result.

The duel with Bale is most relevant with regard to Ronaldo. Jones spent much of his time at White Hart Lane pulling off to the right flank, assisting full-back Rafael, and shepherding the Welshman away from goal. The majority of Jones' clearances, interceptions, tackles and aerial duels came by the touchline, in "Bale's zone".

The Welshman, suffocated by Jones and Rafael, devoid of space and deprived of one-on-one opportunities, became frustrated and ineffective.

Jones, injury permitting, could do a similar job on Ronaldo, though the Portuguese is a far greater threat through the middle, in crowded areas, and on the right wing than Bale is – and Mourinho will move his prized asset around in an attempt to free him.

Sir Alex could also opt to use his arch-disruptor, Antonio Valencia, on the right of midfield. The Ecuadorian has become a better defender than an attacker, as exemplified by the manner in which he nullified Leighton Baines on Sunday, with the left-back attempting around 50% fewer passes than his season average and attempting a cross half as frequently.

Valencia's role would be twofold; first, he would reduce the workload on Jones with regard to tracking Ronaldo, and, secondly, would allow Rafael to get forward. He also brings speed on the counter in a side where genuine pace is at a premium (against the Toffees, he was left furthest up the field on defensive corners, ready to counter).

It seems counterintuitive to triple-mark Ronaldo only to allow the Portuguese's direct opponent, Rafael, to get forward with greater abandon. But the ex-United man does not track back, instead remaining high up the pitch when the opposition have the ball. In the past, particularly for Portugal, this has allowed opposition right-backs to storm forward and overlap.

POSSESSION PIVOTAL FOR UNITED

AVG PASSES PER GAME & SUCCESS RATE

CARRICK

75.2

88.4%

CLEVERLEY

56.4

90.8%

SCHOLES

56

92%

ANDERSON

42.7

86.8%

KAGAWA

40

90.4%

JONES

33.3

80.9%

With Jones capable of covering Rafael's forays, and Valencia occupying either Fabio Coentrao or Marcelo, the Red Devils' Brazilian full-back (who has two goals and three assists in 20 league starts) could find time and space to supply Robin van Persie.

The more that United worry about Ronaldo, the greater the possibility of overlooking the likes of Karim Benzema and Mesut Ozil. The former is Madrid's top scorer in games in which Ronaldo has not scored, bagging six goals, while the latter has struck four times. If United focus too much on Ronaldo, they risk leaving space for the pair to exploit through the middle.

For Madrid, stifling Carrick could be the key to winning the match. United's possession game revolves almost exclusively around the 31-year-old, with Carrick boasting by some distance the highest pass rate in the side, averaging 76.3 per game. Jones, by way of comparison, has averaged just 28.6 passes per game this year.

United's back line isn't blessed with ball-players (the likely back four of Rafael, Rio Ferdinand, Nemanja Vidic and Patrice Evra have averaged a combined 43.9 passes this season), and they could be put under pressure if Madrid employ the same high-pressing strategy that they have used against Barcelona.

Against the Catalan club, Madrid's front four routinely press high up the pitch, allowing Xabi Alonso to gobble up Xavi and deny the Barcelona defence their favoured out-ball. If Madrid replicate that tactic and manage to take Carrick out of the game, the Red Devils could struggle to find a foothold.

As such, it is imperative that United field a disciplined midfielder on the left wing to drop in and support Carrick, while Wayne Rooney will also likely be asked to drop deep. The probable candidates for the left midfield role are Tom Cleverley and Shinji Kagawa.

Cleverley is more defence-conscious, averaging a tackle every 36 minutes compared to Kagawa's 61 and wins possession on a more frequent basis. Additionally, of players to start 10 or more league games for United, the youngster's average of 53 passes per game is second only to Carrick.

While Cleverley would pack the midfield, he would not ever look to run in behind Alvaro Arbeloa or try to beat him down the line. That would leave the Spaniard free to either move infield and crowd out Van Persie (as he did to Sergio Aguero earlier this season), or advance up the pitch and engage Evra – though one significant weakness of Arbeloa's game is his final-third threat and end product.

Kagawa, who plays a pass as frequently as Cleverley and with identical accuracy, would provide more goal threat and force Arbeloa back without sacrificing ball retention, leaving Evra free to worry only about Angel Di Maria.

The attacking passiveness of Madrid's full-backs was exploited handsomely by Borussia Dortmund in the group stages. Jurgen Klopp's side did not press as high as normal but blocked midfield options and, with the full-backs unable to provide a release, pushed the creative emphasis onto the centre-backs. Alonso dropped deep to collect the ball as a result but was then confronted with a scarcity of options ahead of him.

There is no way for either manager to nullify all threats. Focusing on one player, Ronaldo for example, simply grants freedom to another, an Ozil or Benzema. As such, both Mourinho and Sir Alex will have to pinpoint the greatest dangermen and allow the (only marginally) lesser evils.